I. Field of the Invention
The present invention relates to footwear made of synthetic resin materials. More particularly, the present invention relates to a system and method that is used to make multi-color footwear by printing a selected portion of the footwear with a durable decorative pattern.
II. Description of the Related Art
Footwear made from light-weight materials such as closed cell resin have gained popularity in recent years. One of the methods to manufacture such footwear is molding where resin is injected into a mold. The resin solidifies and assumes the permanent shape of a footwear. The temperature decreases in the mold. U.S. Reissue Patent Re. 29,265 and U.S. Pat. No. 3,962,387 both issued to Hendry and incorporated by reference herein describe a closed cell foam plastic molding machine for molding articles made of closed cell foam plastic. The Hendry patents describe extrusion equipment for injection molding of granular thermoplastic materials to make foam products. The foam is provided by mixing an inert gas, such as nitrogen, into molten thermoplastic material. Multiple molds may be used with a given injection machine to facilitate rapid processing with extended cooling times for the individual molds.
U.S. Pat. No. 6,439,536 issued to Piccolo is incorporated herein by reference and describes the special problem of molding shoes with expanding plastic materials. A two piece undercut mold with a one piece core define a mold cavity that is fed through filing channels. Expanding plastics, and particularly ethylene vinyl acetate (EVA), may expand from 20% to 80% by volume upon the opening of such molds, where it is desirable to open the molds quickly to avoid product deformation. Alternative plastics for use in these applications at least include polyurethane and PVC. Lateral through-holes may be formed in the shoe upper by the use of side inserts. The base section and the strap of a sectional footwear may be molded separately. The base section made by injection molding may expand in size when removed from the mold, but it usually shrinks as it cools down. U.S. Patent Publication US 2004/0231190 describes a particular coefficient of expansion that is generally desirable when molding EVA shoes. It also discloses a molding process in which the base section and the strap of the footwear are separately molded and then assembled together.
Shoes made by injection molding usually contain one primary color throughout the entire footwear. The category of EVA foam shoe has been fashionable in Italy for quite some time, and has recently become popular in the United States. Part of the popularity arises from the use of brightly colored foam in making these shoes, for example, in vibrant red, green, blue, yellow, pink, neon or orange. This uniform color scheme may be due to the relative simplicity of plasticizing and injecting raw materials of a single color. However, footwear with multiple colors may be desirable because they are stylistically more attractive.
Printing processes may be described as including the direct formation of an image on a substrate. A transfer process is one that commences with this direct image, which may be printed in the manner of a photonegative image, and transfers the image to a second substrate. Where footwear receives perhaps a greater amount of wear and tear than other types of clothing, it is a challenge to provide a durable printed image on footwear by these processes. Direct printing processes, such as drum or screen printing, usually result in the mere transfer of inks or dyes, which are generally less durable than plastic materials.
U.S. Pat. No. 6,864,033 issued to Nakamura et al. is incorporated by reference herein and describes a multicolor image transfer system. High definition laser or thermal printing occurs upon respective sheets that may be provided as a laminate. The various sheets may be coated with thermally or optically sensitive chemical compositions that react to heat or light by changing color. The chemical compositions are generally compatible for use as plastic coatings. In particular, various polymers are used as binders for thermal printing of transfer images. These chemical compositions are coated onto a multilayer support. The monomer unit(s) of the image transfer layer are preferably the same as the monomer units of the image-forming layer and the image-receiving layer to increase the adhesion of these materials, which correspondingly increases recording sensitivity, image quality and transferability of the image. Vinyl acetal, styrene, butyral, and styrene acrylate are preferred monomer units, which are particularly excellent in sensitivity and transferability to paper. Polymers of these monomer units alone or copolymers with other units are preferably used as the binders, e.g., polyvinyl butyral-based and polystyrene-based resins and vinyl chloride-vinyl acetate copolymers can be exemplified as such polymers.
There exists a need for adapting current manufacturing processes to provide a capability of printing a durable pattern on molded plastic shoes to make multi-color footwear. All references cited in this disclosure are hereby incorporated by reference.